The Complexity of Volatile Terpene Biosynthesis in Roses: Particular Insights into ß-Citronellol Production.

The fascinating scent of rose (Rosa genus) flowers has captivated human senses for centuries, making them one of the most popular and widely used floral fragrances. Despite much progress over the last decade, many biochemical pathways responsible for rose scents remain unclear. We analyzed the floral scent compositions from various rose varieties and selected the modern cultivar Rosa hybrida 'Double Delight' as a model system to unravel the formation of rose dominant volatile terpenes, which contribute substantially to the rose fragrance. Key genes involved in rose terpene biosynthesis were functionally characterized. Cytosolic geranyl diphosphate (GPP) generated by geranyl/farnesyl diphosphate synthase (G/FPPS1) catalysis, played a pivotal role in rose scent production, and terpene synthases (TPSs) in roses play an important role in the formation of most volatile terpenes, but not for geraniol, citral or ß-citronellol. Subsequently, a series of enzymes, including geraniol dehydrogenase (GeDH), geranial reductase (GER), 12-oxophytodienoate reductase (OPR) and citronellal reductase (CAR), were characterized as involved in the transformation of geraniol to ß-citronellol in roses through three successive steps. Interestingly, the ß-citronellol biosynthesis pathway appears to be conserved in other horticultural plants like Lagerstroemia caudata and Paeonia lactiflora. Our findings provide valuable insights into the biosynthesis of rose volatile terpenoid compounds and offer essential gene resources for future breeding and molecular modification efforts.

A novel O-methyltransferase Cp4MP-OMT catalyses the final step in the biosynthesis of the volatile 1,4-dimethoxybenzene in pumpkin (Cucurbita pepo) flowers.

BACKGROUND: Floral scents play a crucial role in attracting insect pollinators. Among the compounds attractive to pollinators is 1,4-dimethoxybenzene (1,4-DMB). It is a significant contributor to the scent profile of plants from various genera, including economically important Cucurbita species. Despite its importance, the biosynthetic pathway for the formation of 1,4-DMB was not elucidated so far. RESULTS: In this study we showed the catalysis of 1,4-DMB in the presence of 4-methoxyphenol (4-MP) by protein extract from Styrian oil pumpkin (Cucurbita pepo) flowers. Based on this finding, we identified a novel O-methyltransferase gene, Cp4MP-OMT, whose expression is highly upregulated in the volatile-producing tissue of pumpkin flowers when compared to vegetative tissues. OMT activity was verified by purified recombinant Cp4MP-OMT, illustrating its ability to catalyse the methylation of 4-MP to 1,4-DMB in the presence of cofactor SAM (S-(5'-adenosyl)-L-methionine). CONCLUSIONS: Cp4MP-OMT is a novel O-methyltransferase from C. pepo, responsible for the final step in the biosynthesis of the floral scent compound 1,4-DMB. Considering the significance of 1,4-DMB in attracting insects for pollination and in the further course fruit formation, enhanced understanding of its biosynthetic pathways holds great promise for both ecological insights and advancements in plant breeding initiatives.

Identification and characterization of cytochrome P450 CYP77A59 of loquat (Rhaphiolepis bibas) responsible for biosynthesis of phenylacetonitrile, a floral nitrile compound.

MAIN CONCLUSION: Cytochrome P450 CYP77A59 is responsible for the biosynthesis of phenylacetonitrile in loquat flowers. Flowers of some plants emit volatile nitrile compounds, but the biosynthesis of these compounds is unclear. Loquat (Rhaphiolepis bibas) flowers emit characteristic N-containing volatiles, such as phenylacetonitrile (PAN), (E/Z)-phenylacetaldoxime (PAOx), and (2-nitroethyl)benzene (NEB). These volatiles likely play a defense role against pathogens and insects. PAN and NEB are commonly biosynthesized from L-phenylalanine via (E/Z)-PAOx. Two cytochrome P450s-CYP79D80 and "promiscuous fatty acid ω-hydroxylase" CYP94A90, which catalyze the formation of (E/Z)-PAOx from L-phenylalanine and NEB from (E/Z)-PAOx, respectively-are involved in NEB biosynthesis. However, the enzymes catalyzing the formation of PAN from (E/Z)-PAOx in loquat have not been identified. In this study, we aimed to identify candidate cytochrome P450s catalyzing PAN formation in loquat flowers. Yeast whole-cell biocatalyst assays showed that among nine candidate cytochrome P450s, CYP77A58 and CYP77A59 produced PAN from (E/Z)-PAOx. CYP77As catalyzed the dehydration of aldoximes, which is atypical of cytochrome P450; the reaction was NADPH-dependent, with an optimum temperature and pH of 40 °C and 8.0, respectively. CYP77As acted on (E/Z)-PAOx, (E/Z)-4-hydroxyphenylacetaldoxime, and (E/Z)-indole-3-acetaldoxime. Previously characterized CYP77As are known to hydroxylate fatty acids; loquat CYP77As did not act on tested fatty acids. We observed higher expression of CYP77A59 in flowers than in buds; expression of CYP77A58 was remarkably reduced in the flowers. Because the flowers, but not buds, emit PAN, CYP77A59 is likely responsible for the biosynthesis of PAN in loquat flowers. This study will help us understand the biosynthesis of floral nitrile compounds.

The Nighttime Fragrance of Guettarda scabra (Rubiaceae): Flower Scent and Its Implications for Moth Pollination.

Floral scent is crucial for attracting pollinators, especially in plants that bloom at night. However, chemical profiles of flowers from nocturnal plants with varied floral morphs are poorly documented, limiting our understanding of their pollination ecology. We investigated the floral scent in Guettarda scabra (L.) Vent. (Rubiaceae), a night-blooming species with short- and long-styled floral morphs, found in the threatened pine rocklands in south Florida, US. By using dynamic headspace sampling and GC-MS analysis, we characterized the chemical profiles of the floral scent in both morphs. Neutral red staining was also employed to determine the specific floral regions responsible for scent emission in G. scabra. The results revealed that G. scabra's fragrance consists entirely of benzenoid and terpenoid compounds, with benzeneacetaldehyde and (E)-ß-ocimene as dominant components. There were no differences in the chemical profiles between the long- and short-styled flowers. Staining assays indicated that the corolla lobes, anthers, and stigma were the primary sources of the scent. These findings indicate that G. scabra's floral scent is consistent with that of night-blooming plants pollinated by nocturnal hawkmoths, providing important insights into its chemical ecology and pollinator attraction. This study demonstrates how floral scent chemistry can validate predictions based on flower morphology in hawkmoth-pollinated plants.

Chemical Attraction of Gall Midge Pollinators (Cecidomyiidae: Cecidomyiinae) to Anthurium acutangulum (Araceae).

Flowering plants often use chemical signals to attract their pollinators, and compounds that elicit attraction are known for several groups of pollinators. For other pollinators such as gall midges, however, compounds responsible for their attraction to flowers are largely unknown. Here, we describe the pollination biology of Anthurium acutangulum, a Neotropical aroid species found to be attractive to gall midges. We collected and analyzed its floral scent by dynamic headspace collections and gas chromatography coupled to mass spectrometry, and identified compounds responsible for pollinator attraction. The inflorescences were almost exclusively visited by gall midges (females; Cecidomyiidae: Cecidomyiinae) and released a strong scent reminiscent of freshly cut cucumber, mainly (5S,7S)-trans-conophthorin, (E2,Z6)-2,6-nonadienal, and cis-conophthorin. Behavioral assays with the two most abundant compounds identified (E2,Z6)-2,6-nonadienal as being highly attractive to the female gall midge pollinators, whereas (5S,7S)-trans-conophthorin was not attractive. Overall, we introduce a new specialized gall midge pollination system and identify the chemical mediating communication between the pollinators and their host plants.

Genome-Wide Identification of Petunia HSF Genes and Potential Function of PhHSF19 in Benzenoid/Phenylpropanoid Biosynthesis.

Volatile benzenoids/phenylpropanoids are the main flower scent compounds in petunia (Petunia hybrida). Heat shock factors (HSFs), well known as the main regulator of heat stress response, have been found to be involved in the biosynthesis of benzenoid/phenylpropanoid and other secondary metabolites. In order to figure out the potential function of HSFs in the regulation of floral scent in petunia, we systematically identified the genome-wide petunia HSF genes and analyzed their expression and then the interaction between the key petunia HSF gene with target gene involved in benzenoid/phenylpropanoid biosynthesis. The results revealed that 34 HSF gene family members were obtained in petunia, and most petunia HSFs contained one intron. The phylogenetic analysis showed that 23 petunia HSFs were grouped into the largest subfamily HSFA, while only two petunia HSFs were in HSFC subfamily. The DBD domain and NLS motif were well conserved in most petunia HSFs. Most petunia HSF genes' promoters contained STRE motifs, the highest number of cis-acting element. PhHSF19 is highly expressed in petal tubes, followed by peduncles and petal limbs. During flower development, the expression level of PhHSF19 was dramatically higher at earlier flower opening stages than that at the bud stage, suggesting that PhHSF19 may have potential roles in regulating benzenoid/phenylpropanoid biosynthesis. The expression pattern of PhHSF19 is positively related with PhPAL2, which catalyzes the first committed step in the phenylpropanoid pathway. In addition, there are three STRE elements in the promoter of PhPAL2. PhHSF19 was proven to positively regulate the expression of PhPAL2 according to the yeast one hybrid and dual luciferase assays. These results lay a theoretical foundation for further studies of the regulation of HSFs on plant flower scent biosynthesis.

A promiscuous fatty acid ω-hydroxylase CYP94A90 is likely to be involved in biosynthesis of a floral nitro compound in loquat (Eriobotrya japonica).

Nitro groups are often associated with synthetically manufactured compounds such as medicines and explosives, and rarely with natural products. Loquat emits a nitro compound, (2-nitroethyl)benzene, as a flower scent. The nitro compound exhibits fungistatic activity and is biosynthesised from l-phenylalanine via (E/Z)-phenylacetaldoxime. Although aldoxime-producing CYP79s have been intensively studied, it is unclear what enzymes form nitro groups from aldoximes either in plants or in other organisms. Here, we report the identification of two cytochrome P450s that are likely to be involved in (2-nitroethyl)benzene biosynthesis in loquat through differential gene expression analysis using RNA-seq and functional identification using yeast and tobacco. CYP79D80 and CYP94A90 catalysed the formation of (E/Z)-phenylacetaldoxime from l-phenylalanine and (2-nitroethyl)benzene from the aldoxime, respectively. Expression profiles of CYP79D80 and CYP94A90 were correlated with the emission of (2-nitroethyl)benzene from loquat flowers. CYP94A90 also functioned as a fatty acid ω-hydroxylase as do other CYP94A fatty acid ω-hydroxylases. The CYP94As tested from other plants were all found to catalyse the formation of (2-nitroethyl)benzene from (E/Z)-phenylacetaldoxime. CYP79D80 and CYP94A90 are likely to operate in concert to biosynthesise (2-nitroethyl)benzene in loquat. CYP94A90 and other CYP94As are 'promiscuous fatty acid ω-hydroxylases', catalysing the formation of nitro groups from aldoximes, and are widely distributed in dicot plants.

The role of sensory drive in floral evolution.

Sensory drive theory posits that the evolution of communication signals is shaped by the sensory systems of receivers and the habitat conditions under which signals are received. It has inspired an enormous body of research, advancing our understanding of signal evolution and speciation in animals. In plants, the extreme diversification of floral signals has fascinated biologists for over a century. While processes involved in sensory drive probably play out in plant-pollinator communication, the theory has not been formally synthesized in this context. However, it has untapped potential to explain mechanisms underlying variation in pollinator preferences across populations, and how environmental conditions impact floral signal transmission and perception. Here I develop a framework of sensory drive for plant-pollinator interactions, identifying similarities and differences from its original conception. I then summarize studies that shed light on how the primary processes of sensory drive - habitat transmission, perceptual tuning, and signal matching - apply to the evolution of floral color and scent. Throughout, I propose research avenues and approaches to assess how sensory drive shapes floral diversity. This framework will be important for explaining patterns of extant floral diversity and examining how altered signaling conditions under global change will impact the evolutionary trajectory of floral traits.

Flower scent of Ceropegia stenantha: electrophysiological activity and synthesis of novel components.

In specialized pollination systems, floral scents are crucial for flower-pollinator communication, but key volatiles that attract pollinators are unknown for most systems. Deceptive Ceropegia trap flowers are famous for their elaborate mechanisms to trap flies. Recent studies revealed species-specific floral chemistry suggesting highly specialized mimicry strategies. However, volatiles involved in fly attraction were until now identified in C. dolichophylla and C. sandersonii, only. We here present data on C. stenantha for which flower scent and pollinators were recently described, but volatiles involved in flower-fly communication stayed unknown. We performed electrophysiological measurements with scatopsid fly pollinators (Coboldia fuscipes) and identified 12 out of 13 biologically active floral components. Among these volatiles some were never described from any organism but C. stenantha. We synthesized these components, tested them on antennae of male and female flies, and confirmed their biological activity. Overall, our data show that half of the volatiles emitted from C. stenantha flowers are perceived by male and female fly pollinators and are potentially important for flower-fly communication in this pollination system. Further studies are needed to clarify the role of the electrophysiologically active components in the life of scatopsid fly pollinators, and to fully understand the pollination strategy of C. stenantha.

Generation of (2-Nitroethyl)benzene and related benzenoids from L-Phenylalanine; flower scents of the Japanese Loquat Eriobotrya japonica [Rosales: Rosaceae].

(2-Nitroethyl)benzene, methyl 4-methoxybenzoate and 4-methoxybenzaldehyde have been known as major scent components in flowers of the Japanese loquat Eriobotrya japonica [Rosales: rosaceae], together with 13 related benzenoids, including Z- and E-2-phenylacetaldoxime and benzyl alcohol. The scents air-trapped from a flowering panicle during 24 h incubation with d8-L-phenylalanine were composed of 15 deuterium labeled compounds {d6-styrene, d5-benzaldehyde, d7-2-phenylacetaldehyde, methyl d5-benzoate, d7 -2-phenylethanol, d7-2-phenylacetonitrile, d4-1,4-dimethoxybenzene, d7-Z-2-phenylacetaldoxime, d4-4-methoxybenzaldehyde, d7-E-2-phenylacetaldoxime, d4-4-methoxybenzyl alcohol, d7-(2-nitroethyl)benzene, methyl d4-4-methoxybenzoate, methyl d6-cinnamate and ethyl d4-4-methoxybenzoate}. On the other hand, hexane extracts of the flower petal incubate with a mixture of d5-Z- and d5-E-2-phenylacetaldoxime after 24 h indicated generation of six d5-labeld components {d5-benzaldehyde, d5-benzyl alcohol, d5-2-phenylacetaldehyde, methyl d5-benzoate, d5-2-phenylethanol, and d5-(2-nitroethyl)benzene}. By comparing those results, (2-nitroethyl)benzene was concluded as a product directly generated from a mixture of Z- and E-2-phenylacetaldoxime together with six minor benzenoids, while two major compounds (4-methoxybenzaldehyde and methyl 4-methoxybenzoate) together with three minors from L-phenylalanine, presumably via L-tyrosine. The other two minor components were derived from L-phenylalanine.

Breeding of fragrant cyclamen by interspecific hybridization and ion-beam irradiation.

Conventional breeding of cyclamen has relied on crossings among Cyclamen persicum cultivars without consideration of the scent of the flowers. Cyclamen purpurascens is a wild species with the most fragrant flowers in the genus Cyclamen. Allodiploid (2n = 2x = 41, AB) and allotriploid (2n = 3x = 65, AAB) plants have been produced from crosses of diploid and autotetraploid cultivars of C. persicum (2n = 2x = 48, AA; 4x = 96, AAAA) × diploid wild C. purpurascens (2n = 2x = 34, BB) by embryo rescue, but are sterile. Fertile allotetraploid (2n = 4x = 82, AABB) plants have been produced by chromosome doubling of the sterile allodiploids in vitro. Autotetraploid C. purpurascens (2n = 4x = 68, BBBB) has been produced by chromosome doubling of diploid C. purpurascens, and other fertile allotetraploids (2n = 4x = 82, AABB) have been produced from crosses of autotetraploid cultivars of C. persicum × autotetraploid C. purpurascens by embryo rescue. Commercial cultivars of fragrant cyclamen have been bred by conventional crosses among the allotetraploids. Mutation breeding using ion-beam irradiation combined with plant tissue culture has resulted in fragrant cyclamens with novel flower colors and pigments. In contrast, allotriploids (AAB) have not been commercialized because of seed sterility and poor ornamental value. The flower colors are determined by anthocyanins and flavonol glycosides or chalcone glucoside, and the fragrances are determined by monoterpenes, sesquiterpenes, phenylpropanoids, or aliphatics. Techniques for the production of fragrant cyclamen and knowledge of flower pigments and volatiles will allow innovation in conventional cyclamen breeding.

Discrimination of Malus Taxa with Different Scent Intensities Using Electronic Nose and Gas Chromatography⁻Mass Spectrometry.

Floral scent is important in plant reproduction and also has aesthetic implications. However, the accurate determination of aroma is presently limited by the available collection and analysis tools. In this study, the floral scents of four crabapple taxa exhibiting faint, weak, clear, and strong scent intensities were comparatively analyzed by electronic nose (E-nose) and gas chromatography⁻mass spectrometry (GC⁻MS). The E-nose was able to effectively group the different taxa in the principal component analysis in correspondence with scent intensity. GC⁻MS analysis identified a total of 60 volatile compounds. The content of nitrogen-containing compounds and aliphatics and the number of unique components of the more aromatic taxa was significantly higher than the less aromatic taxa. α-Cedrene, ß-cedrene, 5-methyl-1,3-dihydro-2H-benzimidazol-2-one, benzyl alcohol, linalool, and 4-pyrrolidinopyridine contributed significantly to taxon separation. The pattern recognition results confirmed that the E-nose results corroborated the GC⁻MS results. Furthermore, partial least squares regression analysis between the aromatic constituents and sensors indicated that particular sensors were highly sensitive to N-containing compounds, aliphatics, and terpenes. In conclusion, the E-nose is capable of discriminating crabapple taxa of different scent intensities in both a qualitative and quantitative respect, presenting a rapid and accurate reference approach for future applications.

Circadian rhythm of a Silene species favours nocturnal pollination and constrains diurnal visitation.

Background and Aims Traits related to flower advertisement and reward sometimes vary in a circadian way, reflecting phenotypic specialization. However, specialized flowers are not necessarily restricted to specialized pollinators. This is the case of most Silene species, typically associated with diurnal or nocturnal syndromes of pollination but usually showing complex suites of pollinators. Methods A Silene species with mixed floral features between diurnal and nocturnal syndromes was used to test how petal opening, nectar production, scent emission and pollination success correlate in a circadian rhythm, and whether this is influenced by environmental conditions. The effect of diurnal and nocturnal visitation rates on plant reproductive success is also explored in three populations, including the effect of the pollinating seed predator Hadena sancta. Key Results The result showed that repeated petal opening at dusk was correlated with nectar secretion and higher scent production during the night. However, depending on environmental conditions, petals remain opened for a while in the morning, when nectar and pollen still were available. Pollen deposition was similarly effective at night and in the morning, but less effective in the afternoon. These results were consistent with field studies. Conclusions The circadian rhythm regulating floral attractiveness and reward in S. colorata is predominantly adapted to nocturnal flower visitors. However, favourable environmental conditions lengthen the optimal daily period of flower attraction and pollination towards morning. This allows the complementarity of day and night pollination. Diurnal pollination may help to compensate the plant reproductive success when nocturnal pollinators are scarce and when the net outcome of H. sancta shifts from mutualism to parasitism. These results suggest a functional mechanism explaining why the supposed nocturnal syndrome of many Silene species does not successfully predict their pollinator guilds.

(2-Nitroethyl)benzene: a major flower scent from the Japanese loquat Eriobotrya japonica [Rosales: Rosaceae].

(2-Nitroethyl)benzene was identified as a major component of the flower scent of the Japanese loquat Eriobotrya japonica [Rosales: Rosaceae], together with p-methoxybenzaldehyde and methyl p-methoxybenzoate. The corresponding volatiles from chopped leaves did not contain these three compounds. This is the first time that 1-nitro-2-phenyl-ethane has been demonstrated to be a natural product among Japanese plants, although two Japanese millipedes are known to possess the same aromatics.

Investigation of genes involved in scent and color production in Rosa damascena Mill.

Rosa damascena Mill., commonly known as the King Flower, is a fragrant and important species of the Rosaceae family. It is widely used in the perfumery and pharmaceutical industries. The scent and color of the flowers are significant characteristics of this ornamental plant. This study aimed to investigate the relative expression of MYB1, CCD1, FLS, PAL, CER1, GT1, ANS and PAR genes under two growth stages (S1 and S2) in two morphs. The CCD1 gene pathway is highly correlated with the biosynthesis of volatile compounds. The results showed that the overexpression of MYB1, one of the important transcription factors in the production of fragrance and color, in the Hot pink morph of sample S2 increased the expression of PAR, PAL, FLS, RhGT1, CCD1, ANS, CER1, and GGPPS. The methyl jasmonate (MeJA) stimulant had a positive and cumulative effect on gene expression in most genes, such as FLS in ACC.26 of the S2 sample, RhGT1, MYB1, CCD1, PAR, ANS, CER1, and PAL in ACC.1. To further study, a comprehensive analysis was performed to evaluate the relationship between the principal volatile compounds and colors. Our data suggest that the rose with pink flowers had a higher accumulation content of flavonoids and anthocyanin. To separate essential oil compounds, GC/MS analysis identified 26 compounds in four samples. The highest amount of geraniol, one of the main components of damask rose, was found in the Hot pink flower, 23.54%, under the influence of the MeJA hormone.

Chemical mimicry of insect oviposition sites: a global analysis of convergence in angiosperms.

Floral mimicry of decaying plant or animal material has evolved in many plant lineages and exploits, for the purpose of pollination, insects seeking oviposition sites. Existing studies suggest that volatile signals play a particularly important role in these mimicry systems. Here, we present the first large-scale phylogenetically informed study of patterns of evolution in the volatile emissions of plants that mimic insect oviposition sites. Multivariate analyses showed strong convergent evolution, represented by distinct clusters in chemical phenotype space of plants that mimic animal carrion, decaying plant material, herbivore dung and omnivore/carnivore faeces respectively. These plants deploy universal infochemicals that serve as indicators for the main nutrients utilised by saprophagous, coprophagous and necrophagous insects. The emission of oligosulphide-dominated volatile blends very similar to those emitted by carrion has evolved independently in at least five plant families (Annonaceae, Apocynaceae, Araceae, Orchidaceae and Rafflesiaceae) and characterises plants associated mainly with pollination by necrophagous flies and beetles.

Loss of Rose Fragrance under Chilling Stress Is Associated with Changes in DNA Methylation and Volatile Biosynthesis.

Rose plants are widely cultivated as cut flowers worldwide and have economic value as sources of natural fragrance and flavoring. Rosa 'Crimson Glory', whose petals have a pleasant fragrance, is one of the most important cultivars of edible rose plants. Flower storage at low-temperature is widely applied in production to maintain quality; however, chilling results in a decrease in aromatic volatiles. To determine the molecular basis underlying the changes in aromatic volatile emissions, we investigated the changes in volatile compounds, DNA methylation patterns, and patterns of the transcriptome in response to chilling temperature. The results demonstrated that chilling roses substantially reduced aromatic volatile emissions. We found that these reductions were correlated with the changes in the methylation status of the promoters and genic regions of the genes involved in volatile biosynthesis. These changes mainly occurred for CHH (H = A, T, or C) which accounted for 51% of the total methylation. Furthermore, transcript levels of scent-related gene Germacrene D synthase (RhGDS), Nudix hydrolase 1 (RhNUDX1), and Phenylacetaldehyde reductase (RhPAR) of roses were strikingly depressed after 24 h at low-temperature and remained low-level after 24 h of recovery at 20 °C. Overall, our findings indicated that epigenetic regulation plays an important role in the chilling tolerance of roses and lays a foundation for practical significance in the production of edible roses.

Deciphering the ecology of the threatened microendemic species Euphorbia margalidiana.

Small islands play a critical role in the study of plant ecology and evolution. Here, we reveal the ecology of Euphorbia margalidiana, an endemic plant that thrives in a micro-island environment in the Western Mediterranean region. Through a detailed characterization of the habitat, including plant communities, microclimate, soil properties, and germination assays, we examine the effects of biotic and abiotic factors on the distribution of this endangered species. We also analyze its pollination biology, evaluate the success of vegetative propagation, and discuss its potential use in conservation strategies. Our results show that E. margalidiana is a characteristic species of the shrub ornitocoprophilous insular vegetation of the Western Mediterranean. The seeds have a very low dispersion capacity outside the islet and that seed-derived plants have higher survival rates under drought conditions than those vegetatively propagated. The main volatile compound emitted from the pseudanthia is phenol which attracts the plants' main and almost exclusive pollinators in the islet, flies. Our results confirm the relictual status of E. margalidiana and highlight the importance of key adaptive traits that enable the survival of this species in the harsh micro-island environment of Ses Margalides.

Floral Scents and Fruit Aromas: Functions, Compositions, Biosynthesis, and Regulation.

Floral scents and fruit aromas are crucial volatile organic compounds (VOCs) in plants. They are used in defense mechanisms, along with mechanisms to attract pollinators and seed dispersers. In addition, they are economically important for the quality of crops, as well as quality in the perfume, cosmetics, food, drink, and pharmaceutical industries. Floral scents and fruit aromas share many volatile organic compounds in flowers and fruits. Volatile compounds are classified as terpenoids, phenylpropanoids/benzenoids, fatty acid derivatives, and amino acid derivatives. Many genes and transcription factors regulating the synthesis of volatiles have been discovered. In this review, we summarize recent progress in volatile function, composition, biosynthetic pathway, and metabolism regulation. We also discuss unresolved issues and research perspectives, providing insight into improvements and applications of plant VOCs.

Five TPSs are responsible for volatile terpenoid biosynthesis in Albizia julibrissin.

Silk tree, Albizia julibrissin Duraz, is an old ornamental plant and extensively cultivated in Asia. Previous works have discovered that the terpenoids were the dominating compounds in the floral VOC of A. julibrissin, however the biosynthesis of these terpenoids was poorly understood so far. Here, 11 terpene synthase genes (TPSs) were identified by transcriptome sequencing that fell into TPS-a, TPS-b and TPS-g subfamilies. The enzymatic activity tests showed that five genes were functional: AjTPS2 was a sesquiterpene synthase and produced α-farnesene and (Z, E)-ß-farnesene; AjTPS5 was able to catalyze the formation of five monoterpenes and nine sesquiterpenes; AjTPS7, AjTPS9 and AjTPS10 were dedicated monoterpene synthases, as AjTPS7 and AjTPS10 formed the single product ß-ocimene and linalool, respectively, and AjTPS9 produced γ-terpinene with other three monoterpenes. More importantly, the main catalytic products of the characterized AjTPSs were consistent with the terpenoids observed in A. julibrissin volatiles. Combining terpene chemistry, TPSs biochemical activities and gene expression analysis, we demonstrate that AjTPS2, AjTPS5, AjTPS7, AjTPS9 and AjTPS10 are responsible for the volatile terpenoids biosynthesis in A. julibrissin.